What's the story on these Bill? There seems to be GTC-85 units everywhere, in all kinds of APU applications. I have two in my start carts. I always amazes me, that they just keep going, and going........

These units are the energizer bunnies. They are very tough units, I remember the AM32-A-60A/B start cart in the Air Force many of these units would shoot flames up ten feet in the air during start up this usually ment re-build time. Even though these engines are tough and will still run with 40% compressor damage the turbine section would not do so good with damage and the flames would show how bad the unit was getting.The GTC-85 engines came in many different dash numbers like, -71, -90, -98, -129, -180, -185, -291 many -60 units had 100 series engines. These little turbine engines create a lot of power, enough for 40 psi 600cfm start air and continuous generator power for the -60 cart. Even with massive damage they would still do the job, of course the more the damage the less the out put. Our AGE equipment folks would pull the units when we complained of fifteen foot flames. I think I remember most of our units belched some flames. I know that our leased unit from AVA sends up a five to six foot flames. That is always alot of fun cranking this unit during the night, when we are out on the desert floor it will light up the mountains. I am always asked is that normal, my reply, "It started up and it's running, its good to go." I figure any turbine enigne that is not spiting parts out is running just fine.

Last edited by f4dj79 on Mon Mar 09, 2009 5:24 pm, edited 1 time in total.

Once again, great info Bill, Thanks.Yep, My MA-1A start cart at the test cell was blowing a flame 10' or so in the air. We replaced the fuel nozzle, and now it's a lot better, only a 4' flame!The compressor must need spruced up, as when we crank the main engines, the cart will only put out about 28 psi of air.

Could I have you re-post your FAA info in the forum on FAA issues please? Thanks.

RobinI know that American Valley Aviation does overhauls on these engines for their GSE refub program. I think they may even do engine swaps provided that the core is not trashed to much. When we went to pick up our unit from them, I talked with the crew at AVA and got an ear full of the problems with these little engines. I found out they have an extensive parts inventory and do alot of in house rework of certain parts. The compressor impellers are getting hard to find. AVA will buy up hundreds of these surplused units and strip the units down and inventory the good parts. Most of the old unit are beat up, that is the reason they are surplused, go figure. I can say that -60 cart we got was just cleaned up, painted and handed over to us. The unit is good shape so I am led to believe that AVA is not putting out any junk. With that being said our cart has some problems that I would like to pass on. First, the unit does work very well if the batteries are not fully charged. Even if you get the unit to start, if the voltage is too low the air diverter valve may not open enough to give 30-40 psi bleed air. The other problem is running these engines on bio-diesel fuel, do not do it! the fuel control is not very adjustable and the bio will clog thing up and then there is that french fry smeel? We have gotten most of the fuel out of the unit but it still is hard to start if it has sat around for awhile. Well that is about all for now.WB

Yeah, the battery thing has caught us out a few times. You're right, they have to be topped right up. I've run the following fuels in my MA1A Cart. The following is a list in order of ease of starting: Jet-A, JP4, P50, Kerosene, No.1 Diesel, No.2 Diesel.No.2 Diesel works ok, with a splash of gasoline added.Never tried bio, and likely won't now.........

Another timely topic. Our test ops with the J79-15's will be located well away from a source of JP-8 or Jet A. How's that engine do with #2 Diesel. Add a touch of gasoline to increase the volatility for an easier light-off?

TerryThat is how I cleaned out the fuel system of the veggie oil. I used clean farm grade Kero (red dye) fuel and white gas (camp stove fuel) it thinned the mix and made it easy to start. Probably raised the BTU's quite a bit, but well within the safe operation level.Now the government uses a high grade of Bio-fuel not the same as bio-diesel. Contact Ed Shadle and see what he is got cooking on fuel for the beast.WB

Actually, if Jet-A is not available, I would spec P50 home heating fuel as Option-1 (A lot cheaper too Basically, Jet-A with slightly higher specific gravity, and less additives.No.1 Diesel would be Option-2 No.2 Diesel, as Option-3. (As Bill says, a little naptha, or straight gasoline added assists lightoff.)

When I have to test run customer's engines on liquid fuel, I use P50, and the engines start and run exactly the same as on Jet-A/JP4 (After adjusting the SG compensator on the FCU)I do not recommend JP8, unless you know it is fresh and you get a great deal, price-wise.

Thanks Robin. Home heating oil will definitely be available in Butte so that's the way we'll go. Actually, JP8 was free during the RASCAL program and we ran the J79-15 source engine, J85-5 test engine, and the F100-200 test engine on it with zero problems; other than the LPT we burned out of the F100. But that was from pure LOX going down the bypass duct. We actually saw -300 F (LOX temperature) on a P2.5 t/c that we had installed. But that was not fuel related but from an operational error in running the facility. The engine was from Pratt's junk yard, anyway. As you also know I've spent some time over the last year going worldwide in a TFE-731-2B Lear 36. We do a lot of military work and get JP8 at all the bases.

RobinThe P50 heating oil is that red dye colored? I believe that we are using the same fuel P50, not just straight kerosene. The cut of fuel is better and is cheaper for sure. I know that our engine runs just fine on it and the SG is so close to JP-8 that even though we have not reset our fuel control from JP-4 we still have good throttle. I tired resetting the SG control on our J79 to JP-8 when we tried the bio-diesel but the engine did not like it to well. Now we are just running P50 with the SG set to JP-4/5 area and the engine likes it just fine. This weekend it's going to be about 40deg. and rainy here in Seattle when we do another test run, I will post the results on the startup and engine operations.WB